ATP Tour Rank: No. 6️⃣ Universal Tennis Rank: No. 4️⃣ What he's done since last summer: Won the ATP Finals Stefanos Tsitsipas clearly needs no introduction. https://www.tennis.com/pro-game/2020/07/21-under-club-2020-edition-stefanos-tsitsipas-atp-finals-champ/89656/

He's the only member of the 21 & Under Club to have beaten Federer, Nadal and Djokovic.